An example of a power supply control device configured to control the supply of power from a battery of a vehicle to a load is a power supply control device in which the drain and the source of an N-channel FET (Field Effect Transistor) are respectively connected to a positive electrode of the battery and one end of the load, and a negative electrode of the battery is connected to the other end of the load. The FET functions as a semiconductor switch in this power supply control device. The FET is switched on by increasing the voltage at the gate to at least an ON-threshold, and is switched off by reducing the voltage at the gate to less than an OFF-threshold. If the FET is on, power is supplied from the battery to the load, and if the FET is off, power is supplied from the battery to the load.
However, a parasitic diode is formed between the drain and the source of the FET. The cathode and the anode of the parasitic diode are respectively connected to the drain and the source of the N-channel FET. Thus, if the positive electrode and the negative electrode of the battery are incorrectly connected to the other end of the load and the drain of the FET, even if the FET is off, current continuously flows from the other end of the load to one end, and there is a concern that the load will operate incorrectly.
Patent Document 1 discloses a power supply control device capable of preventing current from flowing to a load if its battery is connected incorrectly. The power supply control device disclosed in Patent Document 1 includes two N-channel FETs (Field Effect Transistors), and the drain of one of the FETs is connected to the drain of the other FET. A positive electrode of the battery is connected to the source of one of the FETs, and one end of the load is connected to the source of the other FET. A negative electrode of the battery is connected to the other end of the load. The supply of power from the battery to the load is controlled by switching on and off the two FETs together.
The cathode of the parasitic diode provided in one of the FETs is connected to the cathode of the parasitic diode provided in the other FET. Thus, if the two FETs are off, no current flows from the battery to the load irrespective of the battery connection state.